Various stress models have been reported to induce analgesia due to stress. This is a phenomenon, referred to as stress-induced analgesia. Exposureof an animal to stressful stimuli, perceived by the animal as a threatening, emergency condition, except nociception, induces a transient increase in core temperature. This response is often called stress-induced hyperthermia. There is literature data that decrease of pain sensitivity often affects thermoregulatory mechanisms in the threatened organism. The purpose of the present study was to compare changes in pain thresholds and coretemperature after three models of acute stress: immobilization (IS), cold (CS) and hot (HS). Antinociceptive effects were evaluated using the paw pressuretest. The changes in the mechanical nociceptive threshold of the male Wistarrats were measured by analgesimeter. Colonic temperature was measured using a digital thermometer. The obtained results show that after IS, CS and HS there are significant increase in pain thresholds. The most pronounced was the effect in nociception after HS, but this effect was very short. Effects of IS and CS was not so powerful, but they were observed during the whole investigated 30th min period. After three models of stress increase in coretemperature was observed during 15th, 30th and 45th min of the experiment. Only in the beginning of the experiment CS elicits hypothermic effect, while IS and HS significantly increased core temperature, most pronounced for HS. In conclusion IS, CS and HS induced nociceptive and temperature changes in rats, which are with different intensity and continuance.Key words: stress-induced analgesia, core temperature, nociception

This work was supported by Grant from the Bulgarian National Scientific Research Foundation VU-L-04/05.